This invention relates generally to an atomic absorption spectrophotometer and an electromagnetic shut-off valve for use therein, and more particularly to an atomic absorption spectrophotometer suited for measuring trace elements with a good reproducibility and an electromagnetic shut-off valve for use therein.
A sample-atomizing portion comprising a graphite tube furnace has been extensively used as means for atomizing a sample in an atomic absorption analysis. A conventional atomic absorption spectrophotometer of this type comprises a sample-atomizing portion for effecting the drying, ashing (incinerating) and atomization of a sample, a power source operable under the control of a controller so as to supply electric current to the sample-atomizing portion, a first pressure regulator for setting an input pressure of an inert gas (e.g. argon gas), a second pressure regulator for adjusting the flow rate of the inert gas, a movable valve, such as an electromagnetic shut-off valve, controlled by the controller so as to operate in synchronism with the operation of the power source, and a flow meter provided downstream of and communicated to the movable valve so as to measure and monitor the gas flow rate. The power source supplies electric current to the sample-atomizing portion under the control of the controller so as to heat the sample-atomizing portion to temperatures necessary for effecting the drying, ashing and atomization of the sample. This conventional atomic absorption spectrophotometer has a high sensitivity, since the sample is atomized in a highly dense condition in a graphite tube furnace, and the spectrophotometer can make a quantitative analysis of trace elements having a concentration on the order of ppb (10.sup.-9) and having about a weight of about 10.sup.-11 g. Therefore, it is said that a close attention must be paid to the absorption analysis. More specifically, measurements obtained by the atomic absorption spectrophotometer are influenced or affected by the environment in which the spectrophotometer is placed, the contamination of a sample container, variations in sampling amount. Thus, such measurements may be subjected to variations. For example, it is known that when dust in the air, which includes alkaline metals, Si, Zn, Al, etc., is included into a sample, measured values different from an expected value are intermittently obtained to vary widely. If a sample container is even slightly contaminated, the reproducibility of measurements is not expected. Further, when taking a sample from a highly viscous material such as a human serum the amount of the sample is varied, thus making it difficult to achieve a satisfactory reproducibility, which results in variations in measurements. Because of the high sensitivity of a prior atomic absorption spectrophotometer employing a graphite tube furnace, it has been considered unavoidable to intermittently obtain such measurements greatly different from the expected values.
To deal with such variations of measurements, it has been a common practice to effect the measurement two or three times with respect to the same sample and to determine a reliable measured value within a certain range of the variations of two or three measurements.